If you dun plan, you are planning to fail...

Someone just told me this phrase on Saturday at work but it just went into my ears and out it comes again. To a certain extent, I think he is right. But today, I realised it's not true afterall (depending on what subject la).

I planned but becos the plans of others were distrupted, it affected mine too. So does it mean that even if I plan, my plans are subjected to other people's plans and schedules? So does it mean tat in future, I should not plan already cos whether I do it or not, it always changes becos of some reasons...