Let's go over three main topics.
Well to start with...
Supports tend to fall into 3 broad categories based on their overall strategy.
A Commit support, like Blitzcrank, will try to jump on the enemy lane and cause a major advantage. They take the biggest risks and usually, have the largest potential for failure. The goal is to kill the other team.
A Harass support, like Nami, will poke and grind the enemy, focusing on making efficient trades as frequently as possible. They rely on range and skill mechanics. To take damage without receiving it, is the goal.
A sustain support, like Taric, focuses on breaking up any action the enemy lane takes, countering any committed attacks, and canceling out harassment damage. The goal is to help your marksman farm in peace.
Some supports, like
Lulu, can use some or all, of these strategies freely, at the cost of some ability to do each of them.
Second. There is the issue of developing a single champion versus counterpicking.
In League of Legends, it is basically always to your advantage to practice a champion. I have played hundreds of games with Nami, and I am still discovering quirks about her skill kit, items which fit in special circumstances, and I can adapt to changes to the game smoothly... I can say with confidence that Ardent Censer is nice for the move speed, but otherwise the effect is a little weak for its frequency and I prefer using Twin Shadows for its very handy active.
Counterpicking is of course, when one champ's skillset grants it big advantages over another champion. But to gain that advantage, you must be good at at that skillset. An experienced player might make do, or might not.
Morgana is an effective Harass/Sustain support. She is hard-countered by
Karma. This is because Karma's shield can mitigate damage from an ally getting snared and help to dodge skillshots and escape Morgana's ultimate, her Tether can be applied through black shield and will snare if it outlasts it, her Ulted Tether will still regenerate Karma's health even if shielded, and Karma's Q skillshot is a splash attack making it tougher to Black Shield and body-block skillshots for your marksman.
None of this nuance, though, will be apparent to someone playing virtually their first game on Karma. There is no guarantee they will have any advantage at all versus a skilled Morgana player. You also gradually learn ways to fight even counters with enough practice. Like I said, I play a lot of Nami, well... Morgana is a counter to Nami. It is possible to pick a skilled Morgana apart, but not that easy. Her Black Shield means I must wait to deploy tidal wave until it is on cooldown, and always be aware of the risk of a counter-ult engage from a pursuit. You learn where the threats are and have a better chance of handling them.
This might seem very obvious to anyone who has played League a while, but supports in particular feel a need to meet "counterpick" demands. Alistar may very well counter Blitzcrank, but only if you know what you are doing with him. This doesn't alleviate the stress from being ranted at to pick Alistar, if the enemy picks Blitzcrank.
That brings us to the third thing.
No position in the entire game is more stressful than support.
You will have less resources, and less power, and you will be expected to invest it in things that make the team stronger, so you can do more with it. It will stretch your resources like a rubber band. The modern support can become very well funded with plenty of assists and a gold support item, but no position is more likely to get "skunked" and end up 3-5k behind. Some supports are very able to win 1 on 1 fights, contribute powerfully to team skirmishes, and pressure and claim objectives. But not all of them, and not always.
Going into the support position with your eyes open, knowing you are going to be "playing from behind"... is important.
Good luck on the field.