When it comes to designing characters for your story it's a bit like a jigsaw puzzle; finding all the pieces and making them fit together into a coherent whole. As I discussed previously you need to avoid making characters too 'good' or too 'bad' but the jigsaw analogy is also flawed; if someone tried to put together the jigsaw of your life I'm pretty sure they would wind up with several pieces that just refused to fit the big picture.
The thing is people are notably inconsistent and prone to irrationality; and that doesn't allow for the simple action of chance in everyone' lives. I've personally spent almost my entire working career in the electronics career, either repairing computers or working in technical support, except for the three fairly random months I spent selling pensions back in the 90's. It was the product of a fairly odd chain of events; the sort of thing that probably wouldn't occur to you if you were designing me as a character and that's the problem of course; when you design something you expect all the pieces to fit together and in real life they just don't.
The best way to avoid this unnatural consistency is try to be a bit random yourself; visit Amazon and pick through their departments and select some random thing to include in your characters life. or you could just go for a walk and match off people walking by into random, unlikely pair and come up with an odd reason why that you can work into your story and character design. However you go about it try adding a little randomness to your characters and it will bring them that bit closer to reality.