a mill cannot grind with water that is past
Opportunities are useless unless you take advantage of them when they are available or present themselves. A: "I've always wanted to work in Japan. I had a chance to do that a couple of years ago, you know." B: "Well, a mill cannot grind with water that is past, Tom." You should take the chance of starting your own company before you have a mortgage to pay and a family to support—the mill cannot grind with water that is past.
mill cannot grind with water that is past
Prov. Do not waste the opportunities you now have.; Do not waste time wishing for what you had in the past. If you want to go abroad, do it now, while you're young and have the money. The mill cannot grind with water that is past.