When we feed, we must take the life energy of others. It cannot be given. It can be offered freely, but still we must do the taking. This is fundamental to the way in which we must process the energy for use ourselves.
When we draw in energy from another, it is transformed through the feeding process into energy we can assimilate and use. If another, however well-meaning, seeks to force energy into us, it will do us little good. The energy must be assimilated to match our own if we are to benefit from it.
It is very difficult for us to assimilate any energy beyond that of life. Others may draw their strength from the earth, the elements, even the stars, but we are bound to life by our lack of it. Some of us are more disconnected from life than others, and this is reflected in what and how much we can feed from in order to sustain ourselves. Few of us can feed from alternate sources, but when we can, it is a blessing which should not be ignored.