I think most regrets come from not knowing where you want to go in the first place, and just diving in and doing whatever you saw someone else do or something you assumed was a good idea at the time....
...instead of sitting down and thinking about where you want your truck to end up as an end point, or at least an objective.
If someone is very new to the entire scene, they simply may not have a clue as to what's important, or, what an end point might look like, etc.
For those of us who perhaps started off roading back in the 1970's, etc....we sort of had some idea as to what sort of wheeling we planned on being able to do, and, what sort of mods might be worth it, or, less worth it, etc.
It might be like building a house...those of use who have at least LIVED in houses sort of know what they look like, and, after you build a few, you kind of get what goes where, and, what is a worthwhile feature, etc.
If you've never SEEN a house before, and you move into a neighborhood where others' are building their new homes...and one neighbor is telling you you need at LEAST 5 of these things called "Bedrooms" and an equal number of these things called "Bathrooms", and another is telling you that's stupid, all you need is one of each....and you suddenly feel like you should have these things, but, maybe just get 2.5 of each?
So, you and your dog are the only ones going to live in the house you're building...and you make it with 2.5 bathrooms and 2.5 bedrooms.
Later, after learning more about houses, and, what makes sense and what doesn't...you realize the guy with 6 kids, and the single guy, were building what would work for THEM....and, averaging them, did not equal YOU.
The OTHER thing that happens is that options that did not EXIST when making your plans become available....or, disappear before you can implement them. So you plan on lockers, and, no one MAKES a better ratio, so, you do the lockers, and, later find there's now a gear set you WOULD HAVE installed when it was all apart...but, its too late now. Or you see there's a gear set that makes sense, you buy the 35's because you can get some oomph back with the gears... and are saving for the gear set, and, they are discontinued/on infinite back order, etc.
For me, it was MOSTLY a transition from jeeps to X's...and I already knew the types of trails, and, that it would also be a DD that had to carry a lot of equipment, etc. I built the first one ('01) accordingly, and was really happy with it. After ~ 1/2 million miles of happiness and a few slings and arrows of outrageous fortune, it was traded to be a rock buggy for a buddy, and I started an '04.
My basic plan was to simply take the stuff off the '01 and install it on the '04.
Then my buddy finds he can't do the buggy project, and has to move out of state, and my plans to do all this in his shop are dashed, and my work schedule is a giant wet blanket on my mod schedule.
So, NOW, I'm thinking maybe I should have sold the '01, and just installed new parts on the '04...as getting the rusty banged up stuff off the '01 and re-fabbing mounts, etc...is exceeding my time budget.
So, I regret it now.
I bought an '04 so I COULD swap on the '01 parts....but, might have started with a newer 2nd gen, if I knew that swap option wasn't in the cards anyway.