First, we realise that 1 can be split up into infinite parts – $1=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+…$
Hence an infinite parts can also be added up to 1 – $\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+…=1$
And here is the mind-blowing nature of $\infty$.