You have a segment of people that are gonna buy from you no matter what.
You have another segment that is not gonna buy from you for their own reasons.
And in between there is huge segment of people who are still undecided.
Landing page optimization, CvR optimization were created for this big segment. And considering that these people do spend 5 seconds to decide if they are gonna stay on your website or abandon all together, the creatives you choose, the copy, the CTA, the whole experience, need to be close to perfection. In other words, nothing can be left to chance.