With accent marks:
За двумя́ за́йцами пого́нишься – ни одного́ не пойма́ешь.
If you are chasing two hares at once, you won’t catch a single one.
This Russian proverb addresses the problems of multitasking: doing several things at the same time will not give you good results.
The expression dates back to primitive times when hunters were stubbornly chasing just one hare until he was completely exhausted. If you chase two hares at once, giving a respite to one or the other, then soon you will be exhausted yourself and the hares will safely flee.
A close English equivalent of this proverb, although with an opposite meaning, is "to kill two birds with one stone".
Other Russian proverbs
The eyes are scared, but the hands are doing.
In a quiet whirlpool, demons live.
Where it is thin, it breaks.
Live for a century, learn for a century, but die being a fool anyway.
Get your sleigh ready in summer and your (horse-drawn) cart in winter.
The apple never falls far from the tree.
Don't go to the woods if afraid of wolves.
Strike the iron while it's hot.