There is a fair bit of research around employees in a company overcommitting to things in a company. Frankly, it is easy to say yes than say no. The reason for that is, saying no requires a lot of work today, because the word 'no' demands reasons. The reasons are hard and require a lot of understanding around how each aspect of the product works. When you don't have all the information available, people lean towards a 'Yes' because it is simpler for the time-being. It provides short term gratification, pleases the bosses, makes you pleasant, etc. But, usually these commitments are not met.
Agreeing or disagreeing to do something should take equal amount of work. We need to understand context, figure out dependencies, understand customers, know the product in and out.
There is another side to this equation. Where people don't commit or think they are overcommitting because they don't have all the context. This is a fundamental reason why companies don't innovate. When the leadership or teams have this attitude, you have a lot of coasters, who play safe all the time. But what this also does is, it creates laziness in terms of people not willing to stretch themselves to find out what is possible.
I feel that overcommitting is not the biggest issue but not understanding the full scope of the problem is. Also, when we are able to define clearly what the team is committing to deliver and identify it as a stretch as needed, that is a challenge most teams love to take. As leaders, we need to be encouraging of such an environment because companies don't innovate by playing safe all the time.
To avoid the stress and burn out associated with overcommitting, it is important to set a context, create boundaries and identify what are the goals and what are stretches.