restarting and trying over is not a failure in this game - it is hopefully a learning moment. The game has a long learning curve - and you have to remember what works in real life does not always translate in to game play.
As a general rule - never buy aircraft - maybe once you have millions and millions of credits - but even then its better to lease and get more aircraft than buy the existing ones - leases are cheap in comparison to the capital required to buy out an aircraft.
I have started and restarted many times in this game trying to learn. I have had one success on a long term world but it was a very slow slog - i have had one success on a short term world but that is because i learned from my previous experiences on the long term world and took off when it started getting established fast - plus it was old aircraft which i found oddly fun.
So … make some notes - what did you do that was right - what were the best routes that you had - what aircraft did you try - what seating. Then restart and try what worked + try something new - figuring out what aircraft work best on which routes and how to do your planning is half the ‘fun’ its like excel for aircraft