The Halacha is that if one is learning Torah and a mitzva presents itself, he should do the mitzva if nobody else will do it - even though this means he should stop learning.
How do this make sense?
The GREATEST reward for any mitzva is Talmud Torah. So logic would dictate that one doesn't stop his learning to do anything else - ever!!
The explanation is that the reward for the mitzva doesn't determine the law of דחיה - overriding one mitzva for another. Even though Torah study provides the biggest reward dividend - it doesn't matter and one should stop learning to do the mitzva.
Why?
Because that is the will of Hashem. So we have to be moseir nefesh and give up our extra schar and do the mitzva.
That is also why a Kohen Gadol or a Nazir should become טמא מת to bury a מת מצוה and miss bringing their Korban Pesach or circumcising their son [see Nazir 48b]. The severity of missing the Korban Pesach and Bris compounded by the Tumas Meis most certainly outweigh the mere מצות עשה of burying the dead - but no matter. The will of Hashem is to bury the מת מצוה. And as they say in the Classics: ותו לא מידי!!!
[עי' דברי דוד ח"א מאמר כ"ה]
