Nuggets of knowledge

What have been the key nuggets of advice that have stayed with you through your career?

One for me, which is in line to my other Blog on 'War on Waste' (please comment on that too) was the adage that the time of the meeting is not mathematically linked to the journey time to get to it i.e. Even if it's taken a long time to get there it does not mean you can stay for the whole day stringing things out. The meeting duration is set by the value of its output not the time taken to get there 

and one more form a great sage who said to me and others present that the trend is the trend and it will change when it changes. Trends are generally backward looking and we never drive a car solely through the rear view mirror.