TL;DR:
If you're planning to upgrade to a 4K monitor on a macbook, make sure you have a cable / adapter that supports 4K@60Hz! If not, you will have a less-than-ideal experience 🙂
The Monitor:

I was fortunate enough to buy a Samsung U28R55 monitor from my good friend at a very discounted price, and was ecstatic to set it up and hopefully find that all the lines of code that I was viewing before were written in some font similar to wingdings.
This monitor would completely revolutionize the way I use my laptop.
The day comes when the monitor finally arrives, and I found things slightly less than impressive.
Setting up the arm, and getting the monitor mounted was no issue. The monitor has 2 HDMI ports and 1 DisplayPort, and since I have an abundance of HDMI cables, I plugged one in and connected it to my USB-C adapter and waited with baited breath to experience this brand new crystal-clear world.
Aaaand I was surprised to find that the experience wasn't that different from my original 1080p curved monitor.... In fact I actually noticed that the mouse seemed to lag while I was dragging it around the screen; like, there was a slight delay between me moving my mouse and the cursor actually moving on screen.
Did my good friend dupe me into buying this dysfunctional monitor?
There's no way he would've done that. He's way too trustworthy to do something like that, also I'm the DM for our D&D campaign, so surely he'd know that I could just unceremoniously kill off his character as revenge.
Did I somehow mess up the monitor during setup?
I could've sworn I was extremely gentle with it. I placed it off in the corner away from absolutely everything to make sure I never came close to messing it up.
Is my HDMI cable messed up?
Maybe I should've invested an extra $15 to get that gold-plated HDMI cable. Maybe that gold property truly would've made all the difference.
Either way, this monitor experience is not going how I want, and I need to figure out why. After a decent amount of googling, I see someone mention in a random forum thread that my cable is probably the issue and they recommend using a DisplayPort → USB-C cable adapter to resolve it.
Given this information at 8pm, I rush to my nearest Walmart to buy the aforementioned cable. After connecting it to both monitor and laptop, I get a wonderful lag-free experience, and my workstation is saved for the night.
The Best Buy:
So you might've noticed that I said the issue was solved for the night. While I did get monitor working (at what I didn't quite understand at the time was 60Hz refresh rate), It was a bit inconvenient.
I mean now I have to plug in TWO different cables into my MacBook?! This is where I draw the line!
So In trying to reduce redundancy and only having to plug in one cable into my MacBook, I decided to take a trip to Best Buy to see if I could easily pick up some sort of Thunderbolt 3 hub / dock / adapter (or HubDockapter) that I could connect the DisplayPort → USB-C cable adapter to; and then in turn connect the HubDockapter to my MacBook and enjoy all the crispiness of my new 4K monitor.
I want to be sure to highlight, that I still didn't 100 percent understand what I was doing at this point. I was incorrectly thinking that my current HubDockapter just wasn't good enough to support my monitor connection, because it didn't have an extra Thunderbolt 3 port on it. Had I used my critical thought skills a little more, I would've understood what was happening.
So I arrive at my local Best Buy, and I immediately make a beeline to the wall of cables and adapters that I know they have. I'm taking time looking through all the options, reading the packaging and trying to see which HubDockapter would make a difference for me. The general consensus here was that all of them basically seemed the same, and none of them quite fit my apparently specific use case scenario.
I started to think that maybe I'm thinking about this problem all wrong; maybe I'm being a little too specific. I mean it does seem a bit unreasonable to ask for a HubDockapter with more than 1 Thunderbolt 3 port on it, that delivers the same power as the Thunderbolt 3 port for a low cost. Maybe what I actually need is a better HDMI cable so that it's a lot less specific, and I can make one of these HubDockapters fit my needs.
These are the thoughts that went through my mind over the span of the next 20 - 30 minutes, all while I continued to stare at this wall of HubDockapters, carefully reading the packaging of each one to make sure I wasn't missing any features or functionality it offered. And then after a while I got tired of reading and decided the best thing to do in this situation would be to just do a lap around the store, in order to clear my mind.
The Solution:
After a 7-minute walk around the rest of the store, I came back to the wall and unfortunately still didn't have the slightest clue about what I should get to make my setup work. I didn't want to go through the trouble of purchasing something that wouldn't work because honestly the process of having to return something gives me a bit of anxiety.
I once again started reading through all of the small-text on the packaging of the HubDockapters, and this time something caught my eye. On one of the boxes, i saw that the Hub could do 4K@30Hz. Upon reading that, things started to click in my head.
4K@30Hz? Wait of course; monitors have a frame-rate! That "lag" I must've been experiencing was really just 4K@30Hz, and I've never had this issue with my previous setup likely because it was 1080p and basically every HDMI connection must be able to support 1080@60Hz! Everything is starting to make sense!!
With this revelation, I started looking at all the HubDockapaters that supported 4K again, but this time I knew to look specifically to see if it supported 4K@60Hz. And it turns out none of them actually did support 4K@60Hz...
Regardless, my spirit was alight, and I immediately left the Best Buy without purchasing a single thing. Oh I'm sure I looked incredibly weird and confused and mostly suspicious to the staff, but I was just excited that I was finally able to connect those dots!
The Conclusion:
So immediately after getting home, I hit up amazon and started searching for USB-C docks for my MacBook that ideally supported a resolution of 4K@60Hz. I eventually found one that also didn't take a huge chunk of my wallet. I settled on the following dock, and it arrives in about 2 days. There's a low amount of reviews for something a bit pricey, but hopefully it works out!
Ultimately the important realization I made is that moving from a 1080p monitor setup to a 4K monitor setup isn't as simple as just plugging in your HDMI cable (well technically it is, but not if you want good quality). Make sure you know what frame-rates your HubDockapters support before making that switch if you want to preserve your display quality.