Elon Musk and his brother started Zip2 with $28,000 and sold it for $37 million (only their shares) 4 years later.
The success of PayPal shouldn't need explanation. Musk's share: $10 million -> $165 million in 3 years.
SpaceX developed Falcon 1 and 9 basically from scratch for a budget ($300 million) that others use for a single rocket launch. NASA initially estimated that it would have taken them $3.6 billion, a later estimate was still at $1 billion.
Source. They have the cheapest rocket on the market in that size class. They are the largest private rocket manufacturer. They are the only company to ever land an orbital rocket on the ground - something others didn't achieve in decades. Musk's investment of $100 million is now worth billions.
How many car companies did start in the last 50 years and got successful? Tesla did, mainly after Musk got involved, and it has a large impact on the market for electric cars.
SolarCity, mainly based on money from Musk (2006), now has the largest or second largest market share (depending on the source) for photovoltaics in the US.
I don't know if we talk about the same people. Musk has been extremely successful with all his companies. He multiplied his net worth by a factor 1 million in 22 years. If he announces things, he is sure they will work. Not all announced things happened at the earliest time estimate given, right. Delays in big projects are common everywhere. The only really long delay is the Falcon Heavy - but the components of the first one seem to be ready, so a first flight in 2017 is realistic.