Things take as long as they take. Which means, sometimes, a deadline is missed and someone will be let down.
That said, you have a lot of control – over the thing that needs doing, the effort and prioritisation that’s put into it, and the communications with the someone. Even if the worst happens and you fail to keep your commitments, bring them inside the circle so they have a chance to make alternative arrangements.
Good discipline starts with the thing that needs doing. Clarify the scope, the deliverables, the timescales. If you can’t do the thing in time, work out together whether the date is more important than 100% delivery, vice versa, or neither. If it’s the date, cut back on the specification, if the thing is more important, stretch the timeframe.
And always be honest, be direct, show humility.
Skippy strategy: As soon as you know, let them know.
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