Every dog has his day
1) Even the lowest of us at some time has a chance to get revenge on an oppressor, no matter how powerful that oppressor may be. 2) We will all have good luck or success at some point in our lives.
Fortune knocks once at every man's door
We all get at least one good opportunity in life; everybody has the opportunity to be successful in life.
He who hesitates is lost
The person who waits too long loses the opportunity; or, more seriously, delay or indecision may have disastrous results.
Make hay while the sun shines
If we want to make hay, we need sunny weather, so when the sun comes we should take the opportunity to make hay. Thus the proverb suggests that we should make good use of any opportunity while it lasts.
Opportunity only knocks once
We should take an opportunity (or chance) when it comes. According to this saying, it will not come again.
Opportunity seldom knocks twice
Take any opportunity or chance when it comes - it may not come again.
Strike while the iron is hot
Seize the opportunity! When we have the chance to do something, we should do it immediately. Otherwise it will be too late.
The tide must be taken when it comes
We should use all opportunities when they come, before it's too late.