Blacksmiths must shape iron while it's hot.'Strike while the iron is hot ' is used when you have to do something immediately rather than waiting until a later time, because later it might be more difficult. You might be less likely to succeed. Why? Because you start analysing. Your brain will give up a thousand times before you actually take action. So do it now, don't think. Now is the best time.
Definition:do it before it's too late
Example:I really want to be fit. I think I'll strike while the iron is hot and go to the gym even today.