I've worked at companies where this seems to happen often and it usually comes down to two things: 1) Poor communication and/or planning as far as what the end

I've worked at companies where this seems to happen often and it usually comes down to two things: 1) Poor communication and/or planning as far as what the end result was supposed to be. The developer built it the way they thought it was supposed to work, they find out later that it's incorrect or the specifications for it keep changing making the developer add one hack after another to get it to do what it needs to do. They'd probably like to just rewrite the whole thing, but by now it's too late. Jr vs Sr: Sr can see this coming and does whatever he/she can do to minimize it. Doesn't necessarily mean they can stop it from though, it might be too high up the chain of command. 2) Little to no testing. The developer built it and said "done" and then it was passed on to the end user. Anything of any complexity is going to be riddled with bugs if there isn't some kind of QA process in between. Developers typically suck and QAing their own work. Jr vs Sr: Sr has more experience to see possible problems before they become problems and if no QA procedure exists, will at least try to run it by a colleague before claiming it "done".