It’s like this:
Clients who hire creatives to do a job often do so because they lack the ability to do it themselves. In a society where everyone avoids spending money if they can help it, nobody is looking to fork out dollar for work if they could do it on their own for free.
As such, these clients have a tendency to HAVE NO IDEA WHAT IT TAKES TO PRODUCE THE WORK YOU ARE PAID TO PRODUCE. They haven’t invested thousands in an education for your specialist skill. They don’t know about how many hours of your life you have spent honing your craft and developing your abilities specifically so you are the best of the best. They don’t care about how much it costs to run the specialist equipment you need to do the job. The have very little understanding of what a specialist skill actually means.
If, when they demonstrate this lack of understanding, you slap them out of their ignorance and set them straight about it by pointing out all the details that you think are obvious as to why you charge the fees you charge, then great. You’ll hopefully get paid, and they may even go on with their knowledge enriched.
If however, you hand out your work for free then you are basically telling the client that “My skillset is worth nothing.” It utterly devalues your investment in your skill, it devalues your time spent on work and it tells people that you’re not worthy of paid work above entry level employment at minimum wage.
Never work for free. Or, if you must, due to a favour or charitable work, go through the motions of making up an invoice so you can see what a job like that ought to earn you. And, if possible, try and make sure the client sees it.
There’s no shame in just inquiring if something can be done for free, but expecting a creative professional to work for nothing or next to nothing is simply insulting.
It’s about more than just being confident in yourself and your work; it’s a fundamental necessity, to understand the value of the profession you have chosen and to respect the investment you have made into your career.