If in doubt, under promise and over deliver

A company I used to work for had 5 fundamental rules which it asked all it's team members to follow, of which number 3 was "Always deliver what we promise. If in doubt, under promise and over deliver".

I always have this rule in the back of my mind during sprint planning as there is always some degree of doubt when you first estimate a task. Therefore, the estimate is usually slightly higher than the amount of time I think it will take me to do the task.

If I come in early, I've exceeded expectations and if I found it was taken me longer than I thought, I come in on time and have matched expectations.

If I didn't follow that rule at all, I would have been late leading to client frustration and loss of trust in the future so I think it's a nice rule to follow sometimes.

What do you think?