To add to scoreboards comments, which I might add are extremely valid, the aspect of responsibility and the interactions with the ground staff pre-departure are where many of the castigations occur.
It should be no surprise that many of the dispatch and ramp staff are inexperienced, they too are often poorly paid and badly treated by their respective employers. Their aim is to get the aircraft away and move on to their next job. Appreciating the fact they get called to task when aircraft depart late, there is a natural tendency to push the departure along regardless. So when occasional problems occur, because of their lack of experience, they may perceive the problem as a non-issue. Not un-naturally, as Captains, we develop a healthy suspicious cynicism of stories we are told, and become adept at subtle interrogation to ascertain the actual facts rather than the initially presented version.
Anecdotally, I hear some captains are less than subtle with their questioning technique, however in this game we are not there to make friends, we are not there to make on time departures at the expense of safety. We are there solely to ensure our fare paying passengers get safely from A to B, knowing we are accountable for even minor transgressions to the company rules and government regulations, some of which could lead to the loss of your licence, employment, or a big bang in the sky. All of which are most undesirable!
Whilst engineers should not be lumped in the same basket as ramp staff, I like many have come across the odd individual, admittedly in a 3rd world port, who was happy to sign and put both of our licences at risk on a dubious interpretation of the MEL because it was easier. My diplomatic questioning met with little luck, more direct questioning and placing my viewpoint more directly was still not successful. However when I eventually stated that I didn't care what the delay was and I was happy to accept all and any responsibility for the delay while the jet was fixed, he did what was necessary. To a casual observer, I could have appeared overly direct and possibly rude.
Sometimes however, getting through to people needs a gradually escalating dialogue, with the hope they catch on before it gets to the stage of being blunt and direct which some can take offence at.
I am by no means perfect, but I do try and put myself in the other persons shoes, hence the healthy cynical approach to the half story we are often presented with.