I totally agree with you, just imagine an investors doesn't have any discretionary income and the investor start to invest without an emergency fund attached to it, such investor will find it difficult to wait for longer term.
And mostly the newbies that is it coming up with their investment that doesn't have discretionary income, will not be that patient enough to wait for a long term for like 5-20yesrs but with time i know that they will eventually invest in long term because this life one will actually start from somewhere as you can afford believe that you will surely make a changes with respect to time.
To invest is to have income to do so - if you will worry about each part of the investment you put out when you can, it will not end up well.
We just need to invest what we can, when we can - and keep doing it steadily.