I’ve noticed a pattern in which people regularly over-commit to work and consequently regularly under-deliver, and don’t seem able to break the cycle. In fact, their actions seem to perpetuate the cycle.
I remember an influential member of a team I once worked with remarking (often) “we’ve really let these guys [the customer] down”. He would then over-commit to make up for it. Unsurprisingly the team would fail to meet its new, larger commitment, and he’d say it again, feel a little worse and commit us all to a little more work next time. This is not the only time I’ve seen this, and not just in IT.
I think the reasons for this cycle are psychological and are linked to self-esteem. You start off perhaps not 100% confident in your ability to deliver (the team is new, the technology untried, the relationship with the customer in its infancy, etc). You stumble a little on your first delivery and, instead of scaling back, managing expectations and aiming for a smooth and confidence-building second delivery, you feel bad, start committing to more and the cycle of declining self-esteem and over-commitment begins (perhaps “team-esteem” would be a better term). The customer gets nervous and starts to give bad feedback and it all spirals out of control.
If you think this is happening the trick is to reframe the problem:
You are right - you’re letting the customer down - but not by delivering less than you promised. You’re letting the customer down by promising more than you can deliver.