A friend of mine was a simultaneous translator at the UN. The one-way rule, into your native language, is the way they run. She did Russian-English primarily and French-English when needed. She also traveled to UN conferences on scientific topics and boned up on the appropriate vocabulary ahead of time.
She taught simultaneous translation and said that she could tell very quickly which students were likely to succeed. The attrition rate was very high.
As for me, even consecutive translation was exhausting. It's all short-term memory and at the end of the job I rarely remembered any specific content, only general subject matter.
I was informally, as a helpful (I hope) bystander, in a two-step situation in Russia where one person spoke Russian and the other spoke French. I spoke both, but all my translation got mentally mediated through English, since I don't seem to have any neural pathways directly between Russian and French. I was wiped out very quickly.

