When it comes to performing hishtadlus, people invest all their energy; however, less so when it comes to tefillos. A hint to this is from the pasuk (Tehillim 104:21)... "The young lions roar for prey and to request their food from Hashem." When it comes to prayers, it is ... "To request their food from Hashem." But when it comes to hishtadlus, ... the lions roar!
We say in Selichos ... We can explain b'derech tzachus, ... we should make a lot of hishtadlus. What type of hishtadlus should we make? ... tefillos and requests. For that is the primary hishtadlus. (The Maor v'Shemesh writes in the name of Rebbe Mordechai of Neshchiz zt'l, one can fulfill his obligation of hishtadlus with tefillah.)
The Chazon Ish (Maaseh Ish vol.7, 103) said that the primary hishtadlus is tefillah. Sometimes, a person must also do a hishtadlus of action, but if one only does hishtadlus of actions and doesn't do the primary hishtadlus, which is tefillah, he certainly didn't fulfill his obligation of hishtadlus.
