In 2013, when launching Telegram, Pavel Durov presented the messenger as a demonstration of the MTProto Protocol capabilities: "This is not so much a full application as it is a proof of concept for MTProto".
Nowadays, knowing about the success of the private TON ICO and Pavel's purchase of 2000 Bitcoins in 2013, we can assume that Telegram was created as a platform for a larger project. Perhaps this is what Durov had in mind when he said that Telegram is practically a demo of MTProto.
But everything was different. When introducing Telegram in 2013 (around the time when Pavel was forced to leave his Russian social media VK), Pavel Durov rolled out an unfinished product on the market. Minor bugs had to be fixed, while the main goal was to test the MTProto Protocol on a wide audience.
At the beginning of 2014, Telegram was bombarded with new users so intensely its servers went offline for a few hours. Of course, the scalability issue was eventually fixed. The end goal, according to the app founder, was a stable messenger with developed social and geolocation functions.
The MTProto experiment was successful, and Telegram began to acquire not only additional features but also new services that will be combined into a single network called Telegram Open Network.