Creating a Good First Impression
The front cover of your book is the first thing that any potential readers will see before they even go to pick it up, and - to quote another well-known aphorism - "First impressions are the most lasting". It is important, therefore, that the design of it makes the right one, and quickly too, as often their minds will be made up within a couple of seconds.
As was discussed in last month's copy of The "Write" Stuff, one of the biggest pros of self-publishing is the amount of control that you, as the author, have. (If you missed that particular article, you can always catch up here: https://www.rowanvalebooks.com/the-pros-to-self-publishing).
But, unless you have previous publishing experience, or a background in art & design, we would highly recommend that you relinquish some of that control to a professional in this instance.
Consider the initial expense a worthy investment, as a high-quality, professional-looking cover is the best advertisement that your book can have while it is on the shelf.