Converting to percentages makes curves comparable in shape — it does not make the instruments themselves comparable. The same pattern on EUR/USD and on a small coin describes events of entirely different magnitude and origin.
What normalisation discards
Normalisation is a necessary step: without it there is nothing to compare. But it deliberately throws away part of the information, and it helps to know which part.
The magnitude of the move. A half-percent move and a forty-percent move look identical after normalisation. For a currency pair the first is an ordinary day and the second an event of the decade; for a volatile coin it is the other way round.
The instrument's usual volatility. The same apparent "sharpness" means different things on a calm and on a jumpy market: where two-percent candles are normal, a five-percent one does not stand out.
The nature of participants and the trading regime. A round-the-clock market with no weekends and an equity market with overnight gaps are built differently, and identical curves arise in them for different reasons.
Why this matters in practice
Because of it, a shape match between different instruments is weak evidence. It says the trajectories are alike; it does not say the situations are alike.
Transferring conclusions deserves particular caution: "gold rose after this shape, so this stock will" is an argument with everything omitted except the picture.
When cross-instrument comparison does make sense
When the instruments are related in substance rather than only in shape: two currency pairs sharing a currency, two coins from one segment, a stock and its sector index.
There a shape match is backed by a connection, and it stops being a coincidence. Even then it is an observation about the past, not a conclusion about the future.
What to do instead of transferring
Look for analogues on the same instrument. Then the usual volatility, the trading regime and the nature of participants stay the same, and a shape match means more.
If the instrument has little history and no analogues are found, that is an honest answer rather than a reason to widen the search to everything.
A common mistake
Being pleased that "the same shape turned up on ten instruments at once". Most likely the criterion is loose: at a permissive threshold similar trajectories exist everywhere, because markets hold only so many common shapes.