The difficulty is to succeed in making "blobs" or "heaps" that are even and well-shaped. It is tricky gesture to learn, it might seem trivial but it's not: to start with you'll make plenty of mistakes and untidy heaps, but eventually you will become a forcing bag professional.
You will also notice a difference in feel according to the preparation, it's always much easier with a thick preparation like
confectioner's custard (French pastry cream), than with a rather runny one like
macaroon mixture.
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