Never being satisfied.
When you start into this hobby (lol, love how I call this habit a hobby? I'm having a hard time knowing what else to call it), you want to compare yourself to people and things that you want to look like. This is all good and fine, but one must understand that they will NEVER get to what you want to look like, unless you set your goals very low.
When starting out, I suggest you find someone that is obtainable and within reach. Not a mind blowing physique, but one that is doable in a short , one to two year period time. Once that's been achieved and surpassed, do it again. There's going to be a point where you will want to aim high. I'm talking stupidly high. Find a roid user or video game character that you want to look like, and be at peace that you will never get there.
I say this, because MANY times, I find people pleased... too pleased, with how they look. They say things like "this is my goal physique, how I look now." That's failure. Why is it failure? Because if you truly believe this, then what's left to push you? You can skip out on going to the gym, because you're there. You can eat poorly (more often) because you're there. You don't have to lift heavier weight, because you're satisfied with who you've become. FUCK NO. Don't ever do that.
Be humble. If somebody says you have good this or that, know that they don't know your goal. Know that your goal is nothing like what you look like. Sure, you can take a compliment, but be WELL aware that while this or that could be nice, you still have other things to improve on. And you always will.
Even the most perfect of physiques could be improved on. Frank Zane never was pleased with how he looked. In hind site, at 70 years old, he's said he looks back and think "that wasn't half bad." That's an exact quote. Even if you were to ask him now, he would tell you he could have better this or that. You need something to drive you - always.