'Take It One Day At A Time'
This is generally in response to parents despairing and panicking about their child's future. If you're too worried about their future to function or look after your child today, that's not a good thing. But as a long-term pattern, 'taking it one day at a time' is not good either.
If you take it one day at a time, you never get to prepare. Each new issue comes completely unexpectedly. When it's time for your child to go to school, you have no plan to help them fit in that setting. When they move from elementary to high school, or some transition like that, you haven't prepared them for it. When they graduate, you have no plan for after graduation. When you die, you leave behind no guidelines or safeguards for their needs.
If you are the parent of a disabled child, you can't just take it one day at a time. You need to think ahead. For example, one OT talked about starting to work on skills needed for driving with a 14 year old learning disabled teen, because in two years, he'd be wanting to get his license. You should do similar things. Don't panic, just think 'what can I do now to make this upcoming issue easier for my child?'
For example, you could check out potential schools for your 3-4 year old to go to Kindergarten in a few years. Talk to the teachers, watch the classes in progress, take your child for a visit if you're strongly considering it. And you can work with your child, to get them ready. Explain to them what school is about and what it'll be like for them (even if they have little verbal skills, they might understand it). Work with them on specific skills for school, especially things like not aggressing towards other kids, dealing with being away from you, etc. If they really aren't ready to learn what you're teaching, don't push it, but just showing them it may help them figure it out later. You might even want to enroll them in preschool or some other day program, especially if it has a reduced schedule compared with Kindergarten so it's less of an adjustment.
If you realize there are systemic barriers in place that will adversely affect your child, you can work on those before they actually get in your child's way. For example, if your child uses a wheelchair, and the school you're considering is not completely accessible, you can start lobbying and fundraising and such before your child even enters the school. I know one parent who started trying to get her child's school playground wheelchair accessible when the girl was in her early years in that school. A few years later, she was in grade 5, no longer into playing on playground equipment, and that playground was still not accessible. Had her mother started earlier, maybe she could've gotten to play in her school playground.
Taking it one day at a time helps dampen your worries, but you can't prepare for things. If you plan ahead, your road will be easier.