Here are some tips form a diamond jungler:
"if all my lanes are losing" means "if im useless"
lets say you took your first camp and are level 2 now. you had some time to watch your lanes and sometimes, in the first few seconds of the laningphase, there allready is a trade happening or someone is pushing. this means, you can look for an opportunity for a level 2 gank.
now you take your second camp and have another 10-15 or so seconds to check out your lanes. your midlane is losing trades? well, this doesnt translate to "my midlane sucks and loses" but it translates to "the enemy laner will want to try and kill my laner and if im there right that moment, its a free kill for me".
this means if all your lanes are losing, all of them (mostly) are gankable. if a lane is winning, the enemy laner is (mostly) diveable and if all your lanes are neither winning nor losing but establishing good lanecontrol by probably being the stronger earlygame champions or pushing their opposing laners into their towers, you can look to duel the enemy jungler or countergank and collect free kills there.
you can ALWAYS gank someone and you can ALWAYS carry your game. if you play perfect, you will have a 95% winrate even in korean challenger, let alone any lower elo on any lower server.
for example: do you know these situations where you just KNOW FOR SURE that your botlane is getting ganked by enemy lee sin in 10 seconds and you ping them to go back and they just dont and die for free and you call them fucking noobs? well, thats the situation you shouldve been there instead of pinging them back. thats the situation you shouldve gotten triplekill because the enemy team wastes everything to gapclose and initiate and overextend hard and you just come out unexpectedly and crush them. thats how you carry and thats also how you get yourself, your laners and your team fed while at the same time wasting the enemies gold and time and cooldowns.
another example: you gank midlane and get a kill and then you gank toplane and get a kill. this nets 2 kills + 2 assists in gold + some gold avantage due to minions lost for enemies aswell as experience lost.
in some cases, this can snowball your lane or at least tip it in your sides favor if the matchup allows it. (if the enemy champion is a gnar or a kennen and your laner is not a fizz or irelia, most likely this wont change anything. got the point?)
so lets check out the efficiency of this situation: you invested 2 ganks worth of time into gaining about 1000 gold advantage for your team but zero time advantage. its even possible that while you did this, your botlane died to a gank and evened out the gold in only one gank while you invested 2 ganks so your enemy jungler farmed 3 camps more and is now effectively ahead. even if he just farmed alot, he might even be higher level than you now and use this advantage in some way.
other scenario, same example: you countergank your enemy jungler and get two kills for your team. this didnt only negate the entire time-investment of your enemy jungler but it also prevented him from gaining ANY benefit during this time and got you a clean advantage and set back your enemy. you didnt just gain 1000 gold, you also denied your enemy everything.
now you sit at 2:0 and very likely 1-2 levels advantage over your jungler. if you keep track on him and only countergank him from now on, he can never come back into the game and will fall behind more and more. if you do this 2-3 times in a row, he is out of the game, your laners are ahead and you can basically end the game by 17 minutes.
that is what is the meaning of carrying.
if you compare it to reallife: you are in the army and you are on a march through the mountains. you are extremely fit and reach the destination much earlier than your fellow soldiers and you blame them for sucking because look how good and fast you were. that isnt carrying, you did nothing for them and even if you kicked aside some stones on your way so they dont have to, thats really only doing so much for them.
if you want to carry them, you dont have to carry your weight quickly but you also have to carry their weight. you have to take their backpacks on you and still be faster than them and kick stones out of the way and if one of them collapses, you have to pick him up and carry him alongside their backpacks. this is true carrying and it can be done almost every game. and in many games you will notice that you actually get alot of help from your company and sometimes they carry you too.
many people mistake "im strong and faster than you" for true carrying.