The CEO of Celonis, who won customers by sending them handwritten letters, just raised $290 million. Here's the deck he used to sell the AI tool now used by Uber, Airbus and Siemens.

Running a bootstrapped startup is tough, so Alexander Rinke, co-CEO and co-founder of Celonis, tried a quirky way to cut marketing costs: send handwritten letters to would-be clients. He and his team also figured it could be more effective, thinking a typical formal letter to a top exec would routinely be opened and thrown in the garbage by an executive assistant. "We thought if we hand-write the letter and the address on the envelope an executive assistant can't just open it because it might be a personal letter, from a grandmother, a father-in-law or somebody," he told Business Insider. They sent 1,500 handwritten letters to executives of German businesses, dozens of which turned into solid sales leads. Nowadays, Celonis, which uses AI to help businesses evaluate and fix IT processes, doesn't have to worry too much about using offbeat cost-cutting tricks.