The word "hypocrite" originally meant somebody who acts a part on the stage. It has now come to mean "to assume a counterfeit character". Of course nobody would accuse an actor of hypocrisy for acting the required part. That's an actor's job. But if a person "acts a part" in ordinary life then that could well be hypocrisy.
Jesus is censuring hypocrisy in prayer, fasting and giving alms. Prayer, fasting and giving alms are directed to God, often in repentance. They can spring from the realization, attained perhaps slowly and humbly, that I am not the person I should be before God. They come from the heart, as Joel says, broken, not perhaps, in one dramatic moment but by the small, nagging shames of my sinfulness.
My prayer, fasting and especially almsgiving may, for obvious reasons, indeed be seen by others. They are not, however, actually meant for their eyes. They are meant for God since only He knows the heart from which they spring.
If I begin to enjoy the applause when these good deeds are seen, I may slide over the edge into playing to the crowd: I would then be the budding "actor", the hypocrite in the making.
Lord may my deeds be as pure and simple as those of an uncalculating child.