Can someone tell me why there's 3 massagebox appeared upon Bind(<'FocusIn'>)

Question

self.Lowest = tk.Label(self.Frame2,  font=('Arial', 12), text='lower limit', bg='#E8E8E8', bd=7, anchor=W)
self.Lowest.grid(row=4, column=1)
self.Lowest_e = tk.Entry(self.Frame2, font=('Arial', 12), bg='white', bd=5, width=19, justify='left')
self.Lowest_e.bind('<FocusIn>', self.click_standard)
self.Lowest_e.grid(row=4, column=2)

def click_standard(self, event): #
     if self.standards is not None:
         messagebox.showinfo("Notification", "Tolerance values must not be different!")