Fifteen summers of interns and the mistakes that stuck in my memory were almost never ability failures. They were judgement failures, small, avoidable and repeated by different people every single year as if the list were handed down. So here is the list, handed down properly: ten mistakes, why each one stuck and the fix that costs nothing.
The ten
- 1 · The unchecked number. A page goes out where one figure disagrees with the model behind it. Why it sticks: it converts every future page you send into something someone must re-check, which defeats the purpose of you. Fix: tick every number against its source before anyone else sees it, every time, no exceptions for small pages.
- 2 · The silent struggle. Blocked at 2pm, still silently blocked at 8pm, crisis by 10pm. Why it sticks: the problem was free at thirty minutes and expensive at six hours. Fix: the thirty-minute rule from the first-90-days piece, with what you tried attached to the question.
- 3 · The over-promise. 'Twenty minutes' becomes three hours, twice. Why it sticks: your estimates stop being information and people plan around you instead of with you. Fix: quote honestly, then beat your own number.
- 4 · The wrong attachment. Old version, internal comments, or the wrong deal entirely, sent up or, worse, out. Why it sticks: attachment discipline is the cheapest possible test of carefulness. Fix: open the attachment from the sent-item draft and check it is the file you think, every send.
- 5 · The disappearing act. Gone at 7pm without a word while the team works on. Why it sticks: not the leaving, the silence. Fix: the closing loop, anything else before I go, which buys you the evening cleanly.
- 6 · Speaking beyond the station. The intern who offers deal opinions in a client meeting, uninvited. Why it sticks: it makes the seniors manage you in front of the client. Fix: in external meetings, your job is notes and numbers; opinions are for internal debriefs, where they are genuinely welcome.
- 7 · The chat message that travelled. A sarcastic line about a VP, forwarded. Why it sticks: internal chat is written, storable and forwardable and the industry's memory is long. Fix: never type anything you would not want read aloud in the team meeting.
- 8 · Performative hours. Visibly staying late producing nothing, engineering face time. Why it sticks: seniors did the job for years; they can price output against hours instantly and theatre reads as judgement failure. Fix: when genuinely free, ask the staffer for work once, then go home; the staffing article explains why honest capacity beats visible martyrdom.
- 9 · The same mistake twice. Any error, repeated after correction. Why it sticks: the first time is free and expected; the second converts a mistake into a pattern. Fix: the notebook. Every correction gets written down and re-read before similar tasks.
- 10 · Rudeness below the line. Dismissive to an assistant, curt with support teams. Why it sticks: it is reported with total reliability and it is read as character, the same mechanism the final-round failures article describes in interviews. Fix: none needed if you understand that everyone in the building is the interview.
The pattern and the comfort
Read the list again: not one item requires talent to avoid. They are all process and judgement, which means the entire list is controllable before you walk in and the interns who converted, per the conversion article, were rarely the most brilliant; they were the ones who simply never appeared on it. The written version of half these habits, how to send, chase and close loops by email, is the next article on this site. And if you want your own pre-start habits audited against the list by the person who kept it, that is the IBD Recruiting Review.
FAQ
What are the most common intern mistakes in banking?
Unchecked numbers, silent struggling, over-promising deadlines, wrong attachments, leaving without closing the loop and repeating a corrected mistake.
Is it bad to leave the office before the team?
The leaving is fine; the silence is not. The closing loop, anything else before I go, costs ten seconds and buys the evening cleanly.
How do I recover from a mistake as an intern?
Surface it immediately, fix it, write it down and never repeat it. The first instance is free and expected; the second converts a mistake into a pattern.
Former Executive Director in TMT Investment Banking at Nomura and M&A banker at BNP Paribas. Top-rated mentor with 300+ sessions. About
