Summoning Sapience is the act of noticing that you are in a situation where it'd be beneficial to actually think, rather than running on autopilot.
What "actually thinking" means depends on context, but often includes paying extra attention to details of your environment, thinking through the possible ramifications of those details, making a plan, checking if that plan will work, etc.
Summon Sapience is a Rationality skill. Related to Murphijitsu.