I think the numbers of people who try to start up a note business and end up leaving it before they become successful are reflective of all small business IN GENERAL-- that is, the people who quit or fail tend to be the ones who are not willing to put in the work, trial and error, etc. I get an awful lot of calls from people who say they are interested in getting involved in the note business, but then in the same breath they ask me "How quickly can I make money?", i.e. this guy or that guy is not interested in starting unless I can essentially assure them that they can make X thousand dollars in the first 30 days.... Although I have seen that happen, you need to think more "long term' in this business or in any business... and marketing (sourcing) is the big key. It's the same as marketing any product of service-- if you are just starting out, nobody's heard of you yet. Repetition is the key as is exposure in the right places and targeting the right audience.
And, if you have no business acumen at all, you will fail.
I do think running a note business is a fantastic way to generate income from ground zero, especially if you REFER (or broker or whatever you want to call it) notes to institutional investors without putting up any of your own money and learn by watching what they do while you earn money at the same time. No risk. It's actually very beautiful.
But, it's like running any kind of small business-- you need to put in the work. Marketing, accounting, researching, maintaining a website if you have one, etc.-- a small business owner needs to wear many different hats (sure, you can farm some of this stuff out, but you get what I'm saying) and I think you need to ENJOY doing those things, as I do.
I love my job and I've learned more on this "job" than I've learned working anywhere else.
I highly recommend that 'newbie" note people start this part time, which will reduce or eliminate financial pressure while you go though you startup phase.
The "success rate", or speed of development is entirely dependent on your own effort and discipline...if you don't enjoy what you're doing, you won't succeed.
I cringe when I get calls from people who think that all they have to do is place one ad somewhere or send out a few marketing messages in order to make a financial killing overnight. Those people will never succeed in any business and they should just stick with working for someone else.