Picture this: You are up match point. You come to the net with a good approach shot. Your opponent hits a weak defensive lob. You have the entire court available to hit an overhead winner, but rather than doing that you get tight and miss. Not only can this result in frustration and anger but it often causes players to be embarrassed. "How can I miss an easy shot like that at such an important stage of the match?" This can have a crippling effect on your psyche and can cause you to eventually lose the match. Missing easy overheads and fearing the lob are common problems at the recreational level. While overheads might not take place frequently in singles matches, they will often occur at crucial stages of the match. In doubles, lobbing is one of the most used tactics to win points or annoy the opponents and hitting overheads becomes unavoidable. It is therefore crucial that you develop a stable, consistent and powerful overhead. 

You are not going to improve the overhead by thinking about technique during the swing. The overhead is the fastest stroke in tennis. It is over in a few milliseconds, a blink of the eye. What you need to do is LEARN THE REAL FUNDAMENTALS AND MAKE THE OVERHEAD PART OF YOUR TRAINING REGIMEN. If you learn the fundamentals and get your repetitions in, the second-guessing, anxiousness and hesitation are slowly going to start disappearing. Eventually, you will develop an INTUITIVE OVERHEAD. In other words, you will simply set up the overhead perfectly, apply the correct timing and JUST STRIKE THE BALL. Consequently, all the correct technical elements inside the INTUITIVE ZONE of the overhead will be there without you being conscious of them. You will be able to accelerate without hesitation regardless of the score, therefore, greatly reducing overhead errors and increasing the chance of hitting a winner.