The lump of labour fallacy says that there is only a certain amount of work there is to do and that if one person does the job, no one else can do it. This is not true and is a silly idea. To explain it in simple language, imagine you have two people in a room, and you give one of them a big cake to eat. You might think that if one person eats the whole cake, then there won't be any left for the other. But that's silly - if the first person gives some of the cake to the second person, then they both can enjoy some of the cake!
Similarly, there is enough work to go around for everyone, despite what the lump of labour fallacy suggests. Even if one person gets a job, it doesn't mean that there is no work left for anyone else. There are always opportunities to be found, even if it takes some effort to find them.