Certain spirit-side teachers and guides have said that although spiritual progress can be made without incarnating into this physical dimension, experiences able to be undertaken here can greatly enhance that progress. It's also been suggested individuals are keen to undertake earth incarnations of whatever sort, even those we see as extremely challenging. There are two possible extremes. One is that we all reincarnate repeatedly for an undefined 'time' - the 'Spiritist' teaching seen in 'The Spirits' Book' by Kardec, for example. The other is that none of us ever reincarnates. Lying somewhere in that spectrum is actuality I suggest although actuality will likely mean very different things to individuals. I do understand, though, how difficult it is to rationalise the situation given our limited perception and recently I've found myself viewing my own position very differently from the way I used to.