If you can walk, I'll point in the direction you need to walk.
But only if you're close to me, otherwise I'll point in the opposite direction.
If you can't walk, I'll point out what needs to change before you can walk.
Who am I?
Edit: I'll give you a hint with a more accurate version of the last line:
If you can't walk, I'll point sideways.
Here is another hint.
I am something that you see many times every day.
You are:
A crosswalk light.
If you can walk, I'll point in the direction you need to walk.
If you can walk - that is, cross the street - the crosswalk light shows a "walk" sign to indicate the direction you can cross the street.
But only if you're close to me, otherwise I'll point in the opposite direction.
If you're far away from the crosswalk sign and can't cross at that intersection, it will appear to point you down the opposite way.
If you can't walk, I'll point out what needs to change before you can walk.
If you can't walk because there is traffic, most crosswalk signs count down to indicate when you can walk.
Maybe
a shoe
If you can walk, I'll point in the direction you need to walk.
Shoes' tips point forward - the direction you are walking.
But only if you're close to me, otherwise I'll point in the opposite direction.
If you need to walk out of the building, shoes left at the door typically point into the building.
If you can't walk, I'll point sideways.
If one is sitting in a wheelchair and the legs are crooked, shoes may point sideways.
You are
Wisdom
'If you can walk, I'll point you in the direction that you need to walk'
Wisdom help you chose a good path among those you can take.
'But only if you're close to me, otherwise I'll point in the opposite direction'
…but if you are unwise, it is not so reliable.
'If you can't walk, I'll point out what needs to change before you can walk.'
The wise way when you can't go forward is to find a way that will allow you to go forward…
'If you can't walk, I'll point sideways.'
…witch is usually sideways.
I'm not sure about all the details but I think the answer might be
An Airsteward(ess)
Where "walk" really means
Exit, in particular, in case of emergency.
If you can walk, I'll point in the direction you need to walk.
Where the airsteward(ess) stands, and is pointing, indicates the direction you should go to exit an airplane in case of emergency, as long as you are close to the front of the plane.
But only if you're close to me, otherwise I'll point in the opposite direction.
If you are near the rear of the plane then the emergency exit is in the back and you need to go in the opposite direction to where the airsteward(ess) is.
If you can't walk, I'll point out what needs to change before you can walk.
Some people will need to use the side exits on a plane. Often, I think the plan is for the cabin crew to manage the front and back exits and for the passenger in the window seat of the middle aisle to manage the emergency exits there. In this case the airsteward(ess) will point out to that passenger what "needs to change" for an emergency exit to happen.
This answer is quite loose but the idea of back, side and front makes me think that the answer is probably not far away from this.
You are a city intersection.
When you walk towards the intersection, the intersection points you in the right direction.
Once you have crossed the intersection and keep walking, the intersection points in the opposite direction.
When you are at the intersection and stop walking, the cross-streets point sideways.
You are:
a (railway) barrier
If you can walk, I'll point in the direction you need to walk.
if you can walk, the barrier is up and points along the street. They run parallel.
But only if you're close to me, otherwise I'll point in the opposite direction.
as the barrier points up, it will change where it points to depending on your own position to it.
If you can't walk, I'll point out what needs to change before you can walk.
if you can't walk, the barrier will run parallel to the tracks/crossing street and point towards e.g. the traffic, that has to stop first. Or as in the hint: if you can't walk, it'll point sideways.
