Why my OnTriggerEnter2D Doesnt work?

I tried everything and still wont work ;-;

using UnityEngine;
using System.Collections;
public class collision : MonoBehaviour {
     void OnTriggerEnter2D (Collider2D other)
     {
         if (other.gameObject.tag == "Player")
         {
             Debug.Log ("why wont you work ;_;");
         }
     }
}

Two things – make sure at least one of the physics objects that collides has a Rigidbody2D component and that they both have some sort of Collider2D component.

Also, try this instead of what you have:

if ( other.gameObject.CompareTag("Player") )

Hopefully one of those hints will solve the problem for you.

Jay