diff --git a/Engine.Core/Behaviour.cs b/Engine.Core/Behaviour.cs
index 9d41d61..abe8a3d 100644
--- a/Engine.Core/Behaviour.cs
+++ b/Engine.Core/Behaviour.cs
@@ -54,7 +54,7 @@ public abstract class Behaviour : IBehaviour
 
     public bool Assign(IStateEnable stateEnable)
     {
-        if (_initialized)
+        if (Initialized)
             return false;
 
         _stateEnable = stateEnable;
@@ -65,7 +65,7 @@ public abstract class Behaviour : IBehaviour
 
     public bool Assign(IBehaviourController behaviourController)
     {
-        if (_behaviourController is not null)
+        if (Initialized)
             return false;
 
         _behaviourController = behaviourController;
@@ -90,9 +90,6 @@ public abstract class Behaviour : IBehaviour
         if (!Initialized)
             return false;
 
-        _behaviourController = null!;
-        _stateEnable = null!;
-
         Initialized = false;
         return true;
     }
diff --git a/Engine.Core/BehaviourController.cs b/Engine.Core/BehaviourController.cs
index 4201663..3bf59d4 100644
--- a/Engine.Core/BehaviourController.cs
+++ b/Engine.Core/BehaviourController.cs
@@ -87,7 +87,7 @@ public class BehaviourController : IBehaviourController
 
     public bool Assign(IGameObject gameObject)
     {
-        if (_gameObject is not null)
+        if (GameObject.Initialized)
             return false;
 
         _gameObject = gameObject;
diff --git a/Engine.Core/Behaviours/DrawableBehaviour.cs b/Engine.Core/Behaviours/DrawableBehaviour.cs
index d452e70..4b0784a 100644
--- a/Engine.Core/Behaviours/DrawableBehaviour.cs
+++ b/Engine.Core/Behaviours/DrawableBehaviour.cs
@@ -32,7 +32,7 @@ public class DrawableSpriteBehaviour : Behaviour, IDrawBehaviour, IAssignableSpr
 
     public bool Assign(ISprite sprite)
     {
-        if (_sprite is not null)
+        if (Initialized)
             return false;
 
         _sprite = sprite;
diff --git a/Engine.Core/GameManager.cs b/Engine.Core/GameManager.cs
index 83075c4..eb26a8d 100644
--- a/Engine.Core/GameManager.cs
+++ b/Engine.Core/GameManager.cs
@@ -2,6 +2,7 @@ using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Graphics;
 
 using Syntriax.Engine.Core.Abstract;
+using Syntriax.Engine.Core.Exceptions;
 using Syntriax.Engine.Core.Factory;
 
 namespace Syntriax.Engine.Core;
@@ -63,6 +64,8 @@ public class GameManager : IInitialize
         if (Initialized)
             return false;
 
+        NotAssignedException.Check(this, StateEnable);
+
         foreach (var gameObject in GameObjects)
             gameObject.Initialize();
 
@@ -84,7 +87,7 @@ public class GameManager : IInitialize
 
     public bool Assign(IStateEnable stateEnable)
     {
-        if (_stateEnable is not null)
+        if (Initialized)
             return false;
 
         _stateEnable = stateEnable;
diff --git a/Engine.Core/GameObject.cs b/Engine.Core/GameObject.cs
index 373d1bf..8fc6918 100644
--- a/Engine.Core/GameObject.cs
+++ b/Engine.Core/GameObject.cs
@@ -92,17 +92,13 @@ public class GameObject : IGameObject
             behaviour => behaviour.Finalize()
         );
 
-        _transform = null!;
-        _behaviourController = null!;
-        _stateEnable = null!;
-
         Initialized = false;
         return true;
     }
 
     public bool Assign(IStateEnable stateEnable)
     {
-        if (_stateEnable is not null)
+        if (Initialized)
             return false;
 
         _stateEnable = stateEnable;
@@ -112,7 +108,7 @@ public class GameObject : IGameObject
 
     public bool Assign(ITransform transform)
     {
-        if (_transform is not null)
+        if (Initialized)
             return false;
 
         _transform = transform;
@@ -122,7 +118,7 @@ public class GameObject : IGameObject
 
     public bool Assign(IBehaviourController behaviourController)
     {
-        if (_behaviourController is not null)
+        if (Initialized)
             return false;
 
         _behaviourController = behaviourController;
diff --git a/Engine.Core/StateEnable.cs b/Engine.Core/StateEnable.cs
index 7a1a461..1c047cb 100644
--- a/Engine.Core/StateEnable.cs
+++ b/Engine.Core/StateEnable.cs
@@ -29,7 +29,7 @@ public class StateEnable : IStateEnable
 
     public bool Assign(IEntity entity)
     {
-        if (_entity is not null)
+        if (_entity is not null) // TODO: IInitialize Maybe?
             return false;
 
         _entity = entity;