The question that's never asked, but always heard. In the back of our heads, the dark little space that echos loudest when it speaks - you hear a fellow mother, perfectly innocently (probably... Maybe) say 'oh, well my darling cherubic son is sitting unsupported and juggling his baby bottles and counting backwards from 10 in German! He's only 3 weeks old, don't they just grow up so fast?!' while you sit there thinking, oh my GOD, why can he do all that, while my 6 month old is showing absolutely no interest in sitting supported or not? Hell, she's not even babbling! And you're thinking that because you heard 'so what's your baby doing?' or 'is your baby as clever as mine?' when the question was never asked, nor even really implied (probably, we know what some mothers can be like am I right?)
I do the same thing, I think 'why can't my baby do that when (X) can?' and you know what? It's bollocks. Absolute bollocks. People are all different, people all do things and develop differently and babies are people too! So it makes sense that they don't wake up at 6 months to the day and sit upright, crawl and say 'Mother! I am ready for solid food now!' because that's not how life works, not for anyone, not even for tiny wee people who still need their parents to do everything for them.
Perhaps instead of thinking 'why can't my baby do that?' think about all the things your baby has learned as they've grown, be that a little or a lot - what has your baby done that has made you proud? Because I know I'm getting prouder every day of seeing my little girl get really fascinated by a label on her clothes, or that she goes 'mmmmmmmm' when I put the spoon in her mouth - it's the little changes that are happening every day that you need to focus on. Milestones don't matter, because the more you wish for a milestone to happen, just to be like the baby who ice skate at 8 months, the less time you have to notice how your little is growing and changing in small ways every day and before you know it, your baby is a walking, talking tiny hurricane and you forgot to treasure the little things that are happened along the way.