I fly with Ryanair every few weeks and always check before the final click to confirm, but never had any problems.
My DS1 is less careful. He has recently booked 2 flights for the wrong dates and had to change them. One was for a wedding in April, where, he discovered after the event, he had booked the outward flight to arrive the day after the wedding (!). (He managed to change that, not sure how much it cost him)
He didn't learn from that, though - while he was here in Germany a couple of weeks ago he had to get from Berlin to Brussels and had booked on Ryanair, only to discover on arrival at the airport that the date on his boarding pass was a week earlier! So he had to completely re-book at the airport. Cost a bomb, but he could put that on business expenses thank goodness.
So the answer, as others have said, is check, check, and check again. But you still shouldn't have to do it as often as you have said.
Long-haul and more complicated journeys I usually do through our travel agent, just to make sure everything is correct and to be able to pass the buck if anything goes wrong.