I cashed out my 401k, took the penalty and walked away with 90K liquid. I used it for a down payment on a four plex. Waited six months with profit building and the remaining portion of the original 90K and bought a second four plex. After a year I refinanced both four plexus and was able to pull out around $100k in refi money. I used this to pay the down payment on two more four plexus leaving me with a total of four. The third year I rinsed and repeated and pulled more cash out by refi of the last two and bought two more buildings.
I know have 28 total doors spread over six buildings and five years since I cashed out my 401k. I profit more per year than I had in 401k when I cashed it out.
I'm not a CPA, financial expert, stock market broker or even highly educated but I can tell you that there was no chance I would be pulling six figures a year profit from my 401k today if I had left it sitting.
That is the success story side of the coin. Here is the ugly side:
I know more about bed bugs than I ever cared to know. I keep rubber gloves stocked up for peoples toilets when they clog and it saves me $150 drain call. I keep hot water heater burner assembly kits in my truck in case I get the "my hot water heater isn't working" call. I can go on and on.
The point is that yes you can cash out your 401k and turn it into better money. But I promise you it will not be easy. It will be sleepless nights and hard work and cleaning up other peoples messes and your own mistakes as you learn how to manage the business of tenants.
The hard work will pay off if you are willing to do the hard work and learn to read people and treat people the way you want to be treated without letting your business suffer.
But cash out your 401k and treat people poorly including tenants, outsource all of the dirty work to vendors and property management companies and you will have a better chance at the nearest casino.
Good luck and I sincerely wish you the best.