I’m a big believer in the mantra “underpromise, overdeliver”. If you manage someone’s expectations, you generally keep everyone happy, including yourself. I’ve yet to come across a situation where being over-optimistic is the the right strategy.
“Thanks for your feature request, sounds like a good idea. I’ll talk to the developers about it”
“Sorry kids, I can’t buy you that LEGO now. Maybe next month”
“I’m stuck at work. I should be able to leave in 10-15 minutes”
Rakesh Sarin and Manel Baucells, in their book Engineering Happiness, have distilled this idea into a brilliantly simple equation. The formula for happiness.