Why is jump not working in Unity 2D?

Question

C++ / C#

private float speed = 8;
    float jumpForce = 15;
    private bool isGround = false;

    private Rigidbody2D rb;
    private SpriteRenderer sprite; 

    private void FixedUpdate() {
        CheckGround();
    }
    private void Update(){
        if (Input.GetButton("Horizontal")) 
            Run();
        if (isGround && Input.GetButton("Jump")) {
            Jump();
            Debug.Log("Jump");
        }
    }

    private void Awake() {
        rb = GetComponent<Rigidbody2D>();
        sprite = GetComponentInChildren<SpriteRenderer>();
    }
    private void Jump() {
        rb.AddForce(transform.up * jumpForce);
    }
    private void CheckGround() {
        Collider2D[] collider = Physics2D.OverlapCircleAll(transform.position, 0.3f);
        isGround = collider.Length > 1;
        Debug.Log("CheckGround");
    }

The problem according to the debug results is in this line , the expression assigns the value false, although in theory it should be true isGround = collider.Length > 1

Answer 1

And why does it have to be true? For me, this is not obvious - why if we touch more than 1 collider, then we are on the ground?

Answer 2

A very strange way to check the ground. Why not use the built-in features of OnCollisionEnter/stay/exit and check them by tag or name?