Astable multivibrator using transistor

In theory if both side components were identical both sides would reach Vbe threshold at the same time and amplify the collector current and pull down each other's side. But nothing is every perfectly matched so the race is always won by one side first with the smallest RC time constant on the base and/or largest hFE.

As Tony Stewart has explained one of the transistors will turn on first. When it does the voltage on its collector drops causing the voltage at the other end of the capacitor connected there to drop well below 0.6 V. The voltage across the capacitor cannot be changed instantaneously.

This point is also the base of the other transistor so it will remain turned off until the base end of the capacitor charges to 0.6 V through one of the 47 K resistors.

Lets assume Q2 turns on first. When Q2 is off the voltage on its collector the capacitor + plate is about VCC. The voltage on the - plate is about .6 V . When it turns on the collector voltage drops to 0V and the negative plate of the capacitor drops by the same amount (VCC) so the voltage on the base of Q1 is -VCC+.6 V this will firmly turn off Q1 until the negative plate charges to 0.6 V through R3.

When this happens the transistor turns on pulling down the Voltage on its collector and the base of the other transistor connected through the capacitor. Causing that transistor to turn off.

Rinse and repeat.