Earlier quoted context omitted.
That's something I got from my dad as well - dress for the job you want,not the one you have. I also found that dressing well fixes at least some of the age discrimination you face as a young person, you get treated much better while wearing a suit and a tie than when just wearing a t-shirt or a plain shirt.
So if you want a job at google but work at a bank, wear Hawaiian shirts and shorts? Also, over dressing can be as much of a problem as underdressing. If you came to a def interview at say Facebook in a suit, it could get awkward.
Black pants, white shirts. Works everywhere.