reality check

a reality check (something that clarifies or serves as a reminder of reality often by correcting a misconception; check or review to make sure something is consistent, reasonable, etc.) —
реальная / трезвая оценка (ситуации); проверка в реальных условиях; проверка, как обстоит дело в действительности

take a reality check (make a thoughtful reassessment; to check if what may seem a good plan is really practicable) — трезво / реально оценить ситуацию; посмотреть реальности в глаза; трезво оценить реальность

Example: Рeter planned to enroll in four courses at college while continuing to work full-time and be a tour guide on weekends but, taking a reality check, he decided to enroll in one course only.

need a reality check
If you tell someone that they need a reality check, you want them to consider the true situation instead of the way they want it to be.

See also
[спуститься с небес]
[take a long hard look at sth]
[образумить]

Cf.
[смотреть правде в глаза]