how can i animate a player?

I am trying to animate and watched a video about it, but for some reason the code works on a npc, but not on a player:

local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=1574345273"

local trackanimation = nil
local playability = true
function playAnimation(AnimationSource)
    if playability == true then
        local plr = game.Players.LocalPlayer
        trackanimation = plr.Character:WaitForChild("Humanoid"):LoadAnimation(animation)
        trackanimation.KeyframeReached:Connect(function()
            print("Works")
        end)
        trackanimation:Play()
        print("play")
    end
end

script.Parent.MouseButton1Click:Connect(playAnimation)