The biggest challenges facing online marketers?

I consider myself more than competent in social media and online marketing and can definitely put a good enough strategy in place so that at this stage, I don't have to outsource my marketing.

This is time consuming though so ultimately, once my business is more established I'll definitely be using the skills of someone who can give my online marketing the time and attention it requires to be successful.

From managing my online marketing, there are a few challenges I've come across and I wondered if anyone else experienced the same or if you have anything new to add to this list? Would also love to know of any challenges that you've successfully beaten and how?

Social media:
How and when to post. My content is good (Ha, I like to think so!) but with Facebook and Instagram changing their algorithms left, right and centre, it's hard to now know the best times of day to post. I keep testing but this is a definite area of concern for me. I'm also very aware that each of my posts need to have a purpose. Just to get my name in front of my followers isn't good enough and I know I need to stick to a specific strategy to be effective.

Competition:
There is so much 'noise' online these days that it's super hard to stand out from the crowd. I'm always looking for ways to be different which don't include lowering my prices. I think this is where a combination of passion, good service and authenticity come in but I know there is much more to it than that.

Trust:
The internet makes it really easy for people to type with ulterior motives. Are those reviews real? Is that source reliable? Are those people who they say they are? Often, you need to trust your gut and take advice and services from reputable sources only.

Mobile usage:
It's a well-known fact that mobile users are looking for a different experience than PC users. This means that not only is it important to optimise content for mobile viewers, but also to tailor it to make it appropriate.

Retention:
There's no doubt about it but the consumer is fickle these days! One wrong comment and they're hitting the unsubscribe button faster than you can say 'special offer!' Multi-tasking to work on growing our list while providing content to existing subscribers is an essential part of online marketing which can often get overlooked.

Do you have anything to this list as far as challengers for the online marketer go. Or can you provide any solutions to anything I've written above?

Appreciate your input