In a recent appearance on Bloomberg TV, anchor Tom Keene surprised me with this question: “What is your best Apple story?” I said that in the early 2000s I managed to snag a loaner iPod soon after they were released. It was obviously a new, digital version of the ubiquitous 1980s Sony Walkman. At the time, Apple’s shares were trading at $15, with $13 a share in cash on the balance sheet. I did not see a lot of risk in the shares. I pitched it to my firm’s 800 or so brokers, many of whom bought lots of shares.

But I was surprised when soon after, and the shares shot up to $20, the brokers began to sell. “Up big, 33 per cent, gotta ring the bell,” is what I was told. I held on, and finally sold when my “stop loss” order was triggered on a pullback after the shares reached $45, leaving me with a 300 per cent gain. “A triple!” I smugly declared, in what was probably the worst sale I ever made.

In a career filled with other bad trades, missed opportunities and judgement errors, some decisions stand out, not just for the lost money, but for the lessons learned. Here are four examples:

Apple at $15: I may have paid $15 a share, but that was numerous splits ago, which means that had I held onto that Apple stock through last year, my post-split cost basis would have been 26.78 cents per share. That was about $2.4 trillion in Apple’s market capitalisation ago. From this I learned two lessons: the first and obvious one was to avoid too tight stop losses. I was raising my stop with each $10 gain; a $13 stop on a $15 purchase became $23 once the price crossed $25. Volatility guaranteed that such a tight stop would eventually get executed.

But the more important lesson was on how to think long term. I was behaving like the (former) trader I was, and not the investor I had become. Trade management is important, but mine did not properly align with my time horizon or risk tolerances. They (eventually) fell into sync, but it – expensively – took time.

Robinhood’s 2015 seed round: “That is the dumbest investment idea I have ever heard.” That was what I told Howard Lindzon, who runs a small, successful venture fund and has been an early investor in too many tech winners to list, but include Facebook and Twitter. We were sitting outside the Ferry Building in San Francisco and Howard was pitching me on putting money into the seed round of Robinhood Markets, a new app that allowed people to trade stocks for free.

I smugly told Howard that the world was moving from active to passive investing, from trading in individual stocks to exchange-traded funds. Why would I want to own an app that gives trades away for free to young people with no capital? In my defence, Robinhood was totally “off brand” from what I was writing for Bloomberg Opinion and how we were investing at my firm. Plus, Robinhood’s current success is due in large part to bored millennials looking for something to do during the pandemic lockdowns.

I learned several things. One, stay in your lane. My expertise was not in the venture space, so I should have deferred to the pro. Two, beware of recency bias. An earlier start-up Howard and I invested in never found an exit. That “sample set of one” coloured my view. Three, do not assume that any start-up, or even mature company, will look the same in six months, let alone five years later. Failing to recognise these truisms meant that I left a lot of money on the table.

Behavioural insight: when I was pitching Apple to retail brokers to buy for clients, I could not help but notice the certainty of some people’s conclusions about the company’s attempted turnaround. Even my mother, a former real estate agent and stock dabbler, sounded like everyone else when she said to me: “Apple? They are going out of business!” (Note my own smugness in the above examples.)

I have taught myself to pay attention to any trading idea where my knee-jerk reaction is disgust. The reason is because the subject likely reflects all of the bad news that is likely already priced in, not the good news that may come. The lesson to be learnt is in recognising your emotional reaction as revealing a widespread, and potentially wrong, sentiment.

Short the market: short-sellers have become an endangered species on Wall Street, and that is too bad. My firm had a number of shorts heading into 2008: American International Group, Lehman Brothers Holdings and CIT Group. Before those, there was Bear Stearns Cos.

But even getting those trades rights turned out to be missed opportunities. First, we got out too early because there was a constant threat of a “short squeeze” and our positions would be called away at any moment. Second, we did not size the positions correctly. The gains from these positions failed to offset the losses (in dollar terms, not percentages) another portfolio manager had on that were money-losing long positions. These shorts were “high-conviction” trades, and we should have had much more of each.

The lesson is that you must have the courage of your conviction. If you really believe in a trade, it should be meaningful enough to affect your profits. Otherwise, why bother?

I shared my Apple experience on Twitter and was rewarded with wonderful examples of terrible trades. There always seems to be much more to learn from our failures than our successes. Which leads me to this simple question: What was your worst trade? Hit me up at BRitholtz3@Bloomberg.net, and I will share the best worst trade stories in a future column.

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