It is crucial to recognise that those who do experience extraordinary success by investing a lot of money are either very lucky or have made a lot of investments allowing some of them to be profitable and offsetting any losses they may have experienced along the road.
Having just one investment is obviously a risk too, because even if you have managed all the possible risks and have a good idea of how well your investment can work out, it still might not work out due to some unforseen circumstances. The reason most people are successful is because they did not just rely on one investment. I don't mean that relying on one investment is bad, but the risk is that, in some cases, it might not work out the way you have planned it. If one still has other investments in other assets, then they can serve as backup for the non-profiting or low-profiting investment. So, I agree with what you said. Having more investments will even increase how successful you can be because you will always have other investments to support you.
Cheers 🥂, Dr.Bitcoin_Strange 👺👺