I don't agree with focusing on one thing; 3 to 4 businesses as long as you can keep up is good, so if one underperformed, you have 2 or 3 to rely on and make up for your other losses.
I disagree because the focus should be on one thing but you still have to do some diversification now this shouldn't be a business that will need your focus or take your time. Diversification should be in form of investment that you allow your money to do all the work while it pays you. Improving your finances will require you to to make some sacrifices that'll be worth it when it's time. To improve your finances, you shouldn't be throwing away money at every opportunity that you see because that isn't the best way to invest.
Only put your money into an investments after making sure that the investment is a legitimate one and you're getting fooled into losing your money. Value every dollars that you own and the dollars will help you to make more money. To improve your finances, improve the knowledge that you have about what the rich do to make money.