“I know the feeling.”
I know the feeling. expresses empathy based on a similar experience. It is close to I know how you feel., but lighter and more conversational. Frank comforts Tina about her regrets on the eve of the exam.
B1-04 / CEFR B1 / EPISODE 04
Expressing regret and offering help now
SceneThe night before a big exam. Tina's notes are everywhere. Frank has come over with coffee.

WORDS & CONTEXT
I know the feeling. expresses empathy based on a similar experience. It is close to I know how you feel., but lighter and more conversational. Frank comforts Tina about her regrets on the eve of the exam.
Beat oneself up informally means to blame or criticize yourself harshly, rather than literally hit yourself. Frank encourages Tina by pointing out that blaming herself for starting late will not help tonight.
(Be) careful what you wish for. warns that getting a wish may have drawbacks. When Tina wants Frank's discipline, he humorously describes reading an entire dictionary without anyone stopping him, showing the downside of excessive discipline.
Reach for something means to extend your hand toward it. Here it describes automatically reaching for a phone while studying. Don't let me … asks someone to prevent you from doing something; Tina recognizes her weak resolve.