Making Hay
Meaning
To be highly productive for a limited period of time when the opportunity is present.
Example
While in graduate school you may be living as a pauper, but when you get out with your new degree you will be making hay.
Origin
Making Hay is short for Making hay while the sun shines. If you cut or harvest hay during inclement weather (e.g. rain) the hay becomes heavy and hard to rake and bail but even worse it will mold and become useless. You can only make hay while the sun shines.
