No matter if the date you're receiving is in your local timezone and you'll display it in your timezone, sooner or later, the fact that you ignored there was a timezone behind that date will hurt you.
Long gone are the days where ASCII was enough for everyone. Long gone are the days where you can deal with strings with no "weird" or "funny" characters.
"Cognitive dissonance" is a fancy way of saying "I need to remember two (or more) different and contradicting things at the same time to understand this." Keeping those different things in your head creates a cost and it keeps accumulating the more indirect the things are ('cause you'll have to keep all those in your head).
When you're trying to find a solution to your problem, think on the way the data will flow through your code.
At this point, you should at least have heard about how cool functional programming is. There are a lot of concepts here, but at least the very basic ones you should keep in mind.
"The magical number" is a psychology article about the number of things one can keep in their mind at the same time.
"Cargo cult" is a type of cult which appeared in the Melanesia, in which the natives would build their copy of an airplane (no motor, 'cause they didn't have the knowledge to build one -- or even knew what went inside the airplane) in the hopes they would get the same results as a real airplane.
Simple rule: Is the code yours or from your team? Good, you can make any changes you want. Does it come from outside? DON'T. TOUCH. IT.
Most of the times I saw design patterns being applied, they were applied as a way to find a solution, so you end up twisting a solution -- and, sometimes, the problem it self -- to fit the pattern.
A lot of times I heard "We should use the right tool for the job!" Most of those times it was just a way to push an agenda.