The engineer is a tool first and a combatant second. You do not directly win games. You facilitate other players to win for you. You make their job easier in exchange for reduced combat strength. This does not make you a less skilled combatant. You simply have weaker tools for the job but they can still do the job. The engineer is about self sacrifice. Make sure the people you do your hard work for are worth it. If you cannot endure this, go play some other class.
I'll still be here, fixing my teleporter that broke five seconds ago that you just saw and spouted across alltalk "Engineer, put up a teleporter.", even though it has been there all god damned game prior to your little incident.
I'll still be here, despite the assholes who have the gall to tell me exactly what needs to be done with my tools, when I have done the valve maps to DEATH. The sentry doesn't work there because it can be shot, moron.
I'm that asshole who gets you the teleport base setup and DEFENDED on gravel pit offense so you have a less-guarded attack point on both B and C.
If you think I just crouch and beat my sentry while hooked up to my dispenser for life support, or that is what good engineers should do, I have nothing to say to you. Pick a class that is more to your thinking. I'll be over here, helping you secure the god damned win. Go play pyro, get on my teleporter, and do whatever the hell it is you do.
Are you a fellow engineer perhaps? Here's a tip for you. There's more to the world than just your god damned equipment. If your team has eight or more, there's a reason for a second engineer. If his stuff is spitting fire, you might wanna go hit it and fix it for him, because it helps the TEAM, not just you. Unless you are on a 32 man server, rarely ever should there be a 3rd engineer.
Your engineer builds his tools of aid not just to earn points, or to kill enemies. He wants your team to win. Not just you, your team as a whole. Your engineer loves you. He will never say this, admit it, or confess it under torture. Why else would anyone sacrifice proper firepower for tools whose sole purpose are to aid others.
I wrote this post under the influence of 375ml of some very very lovely momokawa organic junmai sake.