Why were boycotts of British goods an effective way for colonists to protest?

Opposing the Townshend Acts in 1767 was one of the most influential ways the Colonists sought to lessen the power the British had over the colonies in the 1760s. The Townshend Acts had several parts to raise revenue for the British off the goods provided by the colonies with little benefit for those same colonies. The Townshend Acts placed indirect taxes on goods brought from Britain to the colonies, but the Colonists protested additional taxes placed on them. The Colonists rebelled against the British government through a series of essays and boycotts. One protest of the Townshend Acts lead to the Boston Massacre of 1770. The boycotts of British goods was a way to organize the colonies into one force to be dealt with against one target, the British government.

The British had superior lethal force on their side and so a full-scale armed uprising by Indian nationalists would've been out of the question. So the anti-colonial movement hit upon a different approach. As part of its non-violent strategy of resistance, it came up with the idea of a boycott of British goods. It was believed that this would impose severe costs on the British economy, costs that could not be sustained over any length of time. In due course, it was hoped that the British would realize that the Raj was no longer viable as an economic unit, that it was more trouble than it was worth.
The boycott initially proved to be a very effective strategy. For centuries, the British had used its control of India to flood the country with cheap, mass-produced goods, thus destroying vast swathes of domestic manufacturing industry. For British manufacturers, especially cloth-producers, India was a captive market and a major driver of the export trade. The leaders of the Swadeshi movement such as Gandhi knew, therefore, that a boycott of British goods would inflict quite serious damage on the imperial economy. At the same time, it was hoped that the boycott movement would also encourage the development of domestic manufacturing, so that Indians would be able to buy Indian goods instead of British.